1. Field of the Invention
The present invention relates generally to lacrosse sticks, and more particularly, to synthetic lacrosse stick heads that have more consistent performance characteristics under variable playing conditions.
2. Description of the Background
In 1970, the introduction of double-wall, synthetic lacrosse heads revolutionized the game of lacrosse. In comparison to the traditional wooden single-wall heads, the synthetic heads imparted a lightness, maneuverability, and flexibility never-before experienced by lacrosse players. These performance advantages greatly enhanced players' skills such as throwing, catching, cradling, and scooping, and brought the sport of lacrosse to new levels of speed and excitement.
FIG. 1 illustrates a conventional molded head lacrosse stick. As shown, lacrosse stick 100 comprises a handle 102 shown in dotted lines, and a double-wall synthetic head 104. Head 104 comprises a generally V-shaped frame having a juncture 106, sidewalls 108 and 110, a transverse wall (or “scoop”) 112 joining the sidewalls at their ends opposite juncture 106, and a stop member 114 joining sidewalls 108 and 110 at their ends nearest juncture 106. As shown, handle 102 fits into and through juncture 106, and abuts stop member 114. A screw or other fastener placed through opening 107 secures handle 102 to head 104.
FIGS. 2 (A & B) illustrates a conventional injection molded goalie head comprising the same components as a field player's lacrosse stick illustrated in FIG. 1 but with different overall shape due to its generally larger dimensions.
The typical features of a lacrosse stick are shown generally in Tucker et al., U.S. Pat. No. 3,507,495, Crawford et al., U.S. Pat. No. 4,034,984, and Tucker et al., U.S. Pat. No. 5,566,947, which are all incorporated by reference herein.
The traditional double-wall synthetic head is an injection-molded, monolithic structure. Examples of suitable synthetic materials well known in the art include nylon, polypropylene (PP), polyethylene (PE), amorphous polar plastics (e.g., polycarbonate (PC)), polymethylmethacrylate (PMMA), polystyrene (PS), high impact polystyrene (HIPS), polyphenylene oxide (PPO), glycol modified polyethylene terphthalate (PETG), acrylonitrile butadiene styrene (ABS), semicrystalline polar plastics (e.g., polyester PET and PBT), polyamide (e.g., Nylon 6 and Nylon 66), urethane, polyketone, polybutylene terephalate, acetals (e.g., Delrin™ by DuPont), acrylic, acrylic-styrene-acrylonitrile (ASA), metallocene ethylene-propylene-diene terpolymer (EPDM) (e.g., Nordel™ by DuPont), and composites. When first introduced, these materials were clearly superior to wood, offering players improved handling and durability. For example, a lacrosse head constructed of DuPont™ ZYTEL ST 801 nylon resin is able to withstand the bending and harsh impacts inherent to competition far better than a traditional wooden stick. As another example, polycarbonate, though having a flexibility similar to wood, is more structurally durable than wood and much lighter and, therefore, easier to handle.
Although the synthetic materials mentioned afford significant performance advantages over wooden sticks, the use of these conventional materials in a one-piece monolithic head limits a manufacturer's ability to provide heads suitable for the modern game. Lacrosse at virtually all levels now has a competitive season stretching from early February through late May, and is played in schools and leagues throughout the world. Additional competitive play occurs during the summer and fall, particularly in many sections of the United States. References in this application to “competitive play”, “competitive sticks” and the like refer to lacrosse games and sticks that are subject to a governing body set of rules and regulations, such as the NCAA for men's lacrosse, US Lacrosse for women's lacrosse, the National Federation of State High School Association for much of high school lacrosse and variations adopted by individual private school and recreational leagues. Such terms do not refer to articles that have some or all of the basic components of lacrosse sticks (e.g. STX “Fiddle STX”) but which due to their overall size, durability, etc. are not intended for use in competitive play.
Because competitive lacrosse is now essentially a year-round activity, lacrosse equipment is subjected to a wide range of climatic playing conditions, especially with respect to temperature and humidity. Playing temperatures can range from 32 F/0 C to 104 F/40 C, and humidity from single digit to near 100%. Thus, there is a need for a competition lacrosse head that will satisfy playing performance needs in extreme as well as moderate climatic conditions.
As noted, conventional men's and women's lacrosse heads have been made with impact modified Nylon 6,6 (PA66-I), commercially known as ZYTEL™ ST 801, which has a good balance of stiffness, light weight, strength, and impact resistance. However, standard commercially available PA66-I has at least two issues affecting its performance: 1) flexibility (i.e., tensile and flexural modulus) variation with temperature; and 2) moisture absorption, which affects material properties, in particular glass transition temperature.
As with most materials, PA66-I has reductions in tensile and flexural moduli as temperature increases (i.e., a reduction in stiffness) and increases in tensile and flexural moduli as temperature decreases (i.e., an increase in stiffness). For the modern lacrosse player, this dynamic results in an overly flexible head in warm temperatures and a very stiff head in colder temperatures. Both of these conditions can affect play negatively. Excessively flexible heads contribute to inaccurate passes and shots, difficulty catching, ineffectual checking, and even goals allowed due to goalie heads flexing excessively during quick movements while attempting saves. Heads that are too stiff tend to be more brittle, which can cause unwanted harsh vibration when catching and checking, loss of “ball feel”, and increased head breakage. Moisture absorption compounds these problems, in part due to a change in the glass transition temperature of PA66-I as it conditions (absorbs moisture).
FIG. 3 is a chart comparison taken from Material Data Sheets for ZYTEL™ ST 801A (generic name PA66-I) in the “dry-as-molded” (DAM) state, and ST 801A moisture-conditioned after molding with Young's modulus, also known as the tensile modulus, shown in gigapascals (GPa) (e.g., kN/mm2). In the “dry-as-molded” (DAM) state, with zero absorbed moisture, the glass transition temperature of PA66-I is approximately 75 deg C. (see data), which is well above playing temperatures. Below the glass transition temperature, the material has fairly constant tensile modulus; above the glass transition temperature tensile modulus is much lower but mostly constant. Near the glass transition temperature, however, tensile modulus drops rapidly.
As a lacrosse head absorbs moisture, which inevitably occurs when it is exposed to the atmosphere, the glass transition temperature of PA66-I drops to approximately 23 deg. C. This condition is much closer to typical lacrosse playing conditions when even small changes in temperature cause very large swings in tensile modulus and therefore head performance. One way this manifests itself is through inconsistent stiffness and flex in heads. In addition, PA66-I loses approximately one-half its tensile modulus as it conditions or absorbs moisture. Since many lacrosse heads are stored in relatively humid environments, such as locker rooms and warehouses, and much of the country plays in climates with high heat and high humidity, the material in conventional heads rapidly absorbs moisture, causing it to become softer over time and more variable with temperature change.
The graphs of FIGS. 4-5 illustrate the point with respect to dry and conditioned ZYTEL 801. The data in FIGS. 4-5 was collected by subjecting both conditioned and non-conditioned head frames to a standard flexibility test. Focusing on the data points at 23 C, a normal lacrosse playing condition, the strain % of Zytel 801 (FIG. 5) is about double that of unconditioned or “dry” Zytel 801 (FIG. 4). Lacrosse heads made from this same material perform similarly as the data describes.
This variability in conventional heads under different playing conditions makes it very hard for players to anticipate their head's performance. For example, with temperature changes such as those discussed, a head could be 50% more flexible when used during a day game than it was during a game the previous night. This lack of consistency and reliability is what the invention addresses, i.e., a reduction in the performance differences of lacrosse heads when exposed to cold and warm temperatures.
It would be greatly advantageous to provide a custom compound designed to counteract the effects of conditioning and temperature change.